Phase-change material heat exchanger

ABSTRACT

A phase-change material heat exchanger includes a frame configured to define a chamber therein and house a first fluid, the first fluid being water. At least one heat exchange element is configured to have a second fluid pass through an interior of the heat exchange element, the at least one heat exchange element moveably retained within the chamber. When the second fluid passes through the heat exchange element at a first temperature, the first fluid changes from a liquid to a solid, and the second fluid exits the heat exchange element at a second temperature that is higher than the first temperature.

BACKGROUND

The subject matter disclosed herein generally relates to heat exchangersand, more particularly, to phase-change material heat exchangers.

Recent advances in the design and fabrication of electronic componentshas dramatically increased their speed and density but has, at the sametime, led to significant challenges for thermal engineers seeking toprovide heat-transfer solutions for such components.

In some applications, phase-change material heat exchangers may be usedfor high capacity and high energy applications. A phase-change materialused in such heat exchangers is a substance with a high heat of fusionwhich, melting and solidifying at a certain temperature, is capable ofstoring and releasing large amounts of energy. Heat is absorbed orreleased when the material changes from solid to liquid and vice versa;thus, phase-change materials are classified as latent heat storage unitsand provide excellent media in heat exchangers for rapid cooling.

For example, in traditional phase-change material heat exchangers, waxmay be used as the phase-change material. The heat of fusion needed tomelt wax is often used to remove heat from operating systems and/oroperating fluids. As heat is applied or transferred to the wax fromanother medium, such as an operating fluid, normally in a heat exchangerconfiguration, the wax melts. This phase change in the wax, from a solidto a liquid, removes heat from the operating fluid passing through theheat exchanger, thus lowering the operating fluid temperature. After thewax is melted, it may then be re-frozen, and converted back to a solid,so that the heat transfer process may be repeated multiple times. Theamount of energy translated depends on the property “heat of fusion” ormelting energy.

SUMMARY

According to one embodiment a phase-change material heat exchanger isprovided. The heat exchanger includes a frame configured to define achamber therein and house a first fluid, the first fluid being water. Atleast one heat exchange element is configured to have a second fluidpass through an interior of the heat exchange element, the at least oneheat exchange element moveably retained within the chamber. When thesecond fluid passes through the heat exchange element at a firsttemperature, the first fluid changes from a liquid to a solid, and thesecond fluid exits the heat exchange element at a second temperaturethat is higher than the first temperature.

In addition to one or more of the features described above, or as analternative, further embodiments may include that the at least one heatexchange element includes a plurality of surface area structures on anexterior surface thereof.

In addition to one or more of the features described above, or as analternative, further embodiments may include that the plurality ofsurface area structures are at least one of fins and pins.

In addition to one or more of the features described above, or as analternative, further embodiments may include that the at least one heatexchange element has a plate configuration.

In addition to one or more of the features described above, or as analternative, further embodiments may include that the at least one heatexchange element is configured to define a freeze front of the firstfluid along an exterior surface of the at least one heat exchangeelement.

In addition to one or more of the features described above, or as analternative, further embodiments may include that the second fluid is anoperating fluid for a high powered laser.

In addition to one or more of the features described above, or as analternative, further embodiments may include that the frame defines atapered shape with a bottom of the frame being narrower than a top ofthe frame.

In addition to one or more of the features described above, or as analternative, further embodiments may include at least one expansionelement configured to support the at least one heat exchange elementwithin the chamber.

In addition to one or more of the features described above, or as analternative, further embodiments may include that the at least oneexpansion element is a spring.

In addition to one or more of the features described above, or as analternative, further embodiments may include a membrane retained aboutthe frame and configured to expand when the first fluid changes from aliquid to a solid.

In addition to one or more of the features described above, or as analternative, further embodiments may include that the at least one heatexchange element comprises a first support and a second support, with abody extending between the first support and the second support.

In addition to one or more of the features described above, or as analternative, further embodiments may include an enclosure, wherein theenclosure includes the frame and at least a portion of the enclosure isconfigured to expand in response to water freezing.

According to another embodiment, a method of using a phase-changematerial heat exchanger is provided. The method includes conveying anoperating fluid at a first temperature through at least one heatexchange element, the at least one heat exchange element disposed withina chamber of a phase-change material heat exchanger, the chamber filledwith water, causing the water to phase change from a liquid to a solidwithin the chamber, and conveying the operating fluid out of the atleast one heat exchange element at a second temperature that is higherthan the first temperature.

In addition to one or more of the features described above, or as analternative, further embodiments may include conveying the operatingfluid through the at least one heat exchange element at a thirdtemperature when the chamber is filled with ice.

In addition to one or more of the features described above, or as analternative, further embodiments may include that the third temperatureis a temperature sufficiently high to phase change the ice to liquidwater when passing through the at least one heat exchange element.

In addition to one or more of the features described above, or as analternative, further embodiments may include forming a freeze frontprogression within the chamber such that a volumetric expansion of thewater when freezing does not damage the phase-change material heatexchanger.

Technical effects of embodiments of the present disclosure includeproviding a phase-change material heat exchanger that employs water asthe phase-change material, with ice serving as the absorbing phase ofthe material to cool an operating fluid, and during this process the icemelts to become water.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter is particularly pointed out and distinctly claimed atthe conclusion of the specification. The foregoing and other features,and advantages of the present disclosure are apparent from the followingdetailed description taken in conjunction with the accompanying drawingsin which:

FIG. 1 is a partial cut-away schematic illustration of a phase-changeheat exchanger in accordance with an embodiment of the presentdisclosure;

FIG. 2 is a schematic illustration of a phase-change heat exchanger inaccordance with another embodiment of the present disclosure showing anexample flow path of an operating fluid;

FIG. 3 is a schematic illustration of a heat exchange element inaccordance with an embodiment of the present disclosure;

FIG. 4A is a first example of a surface area structure configuration inaccordance with the present disclosure;

FIG. 4B is a second example of a surface area structure configuration inaccordance with the present disclosure;

FIG. 4C is a third example of a surface area structure configuration inaccordance with the present disclosure;

FIG. 4D is a fourth example of a surface area structure configuration inaccordance with the present disclosure; and

FIG. 5 is a process in accordance with an embodiment of the presentdisclosure.

DETAILED DESCRIPTION

Traditionally, wax has been used as a phase-change material inphase-change material heat exchangers because there is a minimal volumechange in wax when changing from a liquid to a solid, and yet the waxhas a relatively high heat of fusion. As such, wax configurations haveenabled phase-change material heat exchangers to work relativelyefficiently without providing increased structural components tocompensate for volume expansion during phase changes of the phase-changematerial. The wax would be enclosed within the heat exchanger, andthermal expansion is managed as known in the art.

In contrast, water/ice has a much higher latent heat or heat of fusionas compared to wax, and thus is more desirable in terms of thermalefficiency. For example, paraffin wax that may be used as a phase-changematerial in heat exchangers has a heat of fusion of 63.2 BTU/Lb_(m),whereas ice has a heat of fusion of 144 BTU/Lb_(m). The much greaterheat of fusion of water/ice is desirable for high energy applications,as a cooling process may occur at a much higher rate, and/or a smallerheat exchanger may be used for the same amount of thermal transfer. Anexample of a high energy application may be a high powered laser thathas a high discharge rate and thus may require a fast cool-down periodof an operational fluid used to cool the laser components.

The problem with employing water/ice as a phase-change material,however, has been the volumetric expansion of the water that occursduring the phase change between a liquid and a solid. The volumeefficiency of water as a phase-change material is 227% greater thanparaffin wax, but water expands almost 10% by volume as it freezes andchanges to ice. Further, the forces of expanding ice are extremely high,having the ability to overcome most enclosing structures. For example,if a heat exchanger volume is filled with water, and the water freezes,the force of the volume expansion of the ice may be sufficient todamage, break, or destroy the housing structure. As such, water/ice is aproblematic material in a phase-change material heat exchanger.

However, in accordance with embodiments disclosed herein, water/ice maybe employed as the phase-change material in a phase-change material heatexchanger, without the risk of damage to the heat exchanger structure.FIG. 1 is a partial cut-away schematic illustration of a heat exchangerin accordance with an embodiment of the disclosure. Heat exchanger 100is a phase-change material heat exchanger configured to employ ice as aphase-change material in order to cool an operating fluid that passesthrough heat exchange elements 106 of the heat exchanger 100. That is,during operation, heat exchanger 100 may be filled with ice, and as ahot operating fluid passes through the heat exchanger 100, the ice maymelt and change to water, thus absorbing large amounts of thermal energyfrom the operating fluid. In preparation of this operation, the heatexchanger 100 must be filled with ice, not water, and thus water withinthe heat exchanger 100 must be frozen.

The heat exchanger 100 is configured to allow a phase-change material,such as water, to expand relatively unrestrained during the phase changeto a solid, i.e., to ice. This is achieved by the heat exchanger 100including a frame 102 that defines a chamber 104 therein. The frame 102may form a tank or other similar structure that may form fluidlycontained chamber or volume, such as a bath. The chamber 104 may beconfigured to house one or more heat exchange elements 106. The heatexchange elements 106 may be plate heat exchange elements, as shown inFIG. 1. In alternative embodiments, the shape, geometry, andconfiguration of the heat exchange elements 106 may be varied, forexample, in some embodiments the heat exchange elements may beconfigured as tubes in a shell-and-tube heat exchanger, or in otherconfigurations known in the art or that may become known.

In the embodiment shown in FIG. 1, the heat exchange elements 106 areconnected to each other by expansion elements 108. The expansionelements 108 may be springs, rods, wires, etc., that are configured toenable the heat exchange elements 106 to be able to move relative toeach other. For example, the expansion elements 108 are configured toallow for the heat exchange elements 106 to move apart from each otherduring a freezing of water contained within the chamber 104. As thewater freezes, it may push outward on the heat exchange elements 106,and the expansion elements 108 permit the heat exchange elements 106 tomove without damage occurring thereto. The expansion elements 108 mayalso be configured to provide shock or vibration absorption or reductiondue to movement of the heat exchanger 100, such as when installed on avehicle.

The heat exchange elements 106 may include structures or configurationsthat increase or optimize the surface area of the heat exchange elements106. For example, as shown, surface area structures 110 may beconfigured in the form of fins or ridges. The fins may optionally be inthe form of perforated folds, as described below. In alternativeembodiments, the surface area structures 110 may be formed as pins,blades, corrugations, grooves, channels, etc. Those of skill in the artwill appreciate that the surface area structures of the heat exchangeelements may be any shape, geometry, and/or configuration that may beconfigured to increase the thermal transfer through a surface of theheat exchange elements 106.

As shown in FIG. 1, the frame 102 is configured having an expandingcross-section as the elevation changes from the base to the top of theheat exchanger 100. This allows an ice front to grow and expand, movingup the frame 102. The frame 102 may be formed from a polymer or othermaterial that enables the frame 102 to deflect to increase the internalvolume without exceeding the plastic limit of the frame 102. Further, amembrane 112 may line the chamber 104 within the frame 102. The membrane112 may be configured to allow the volume contained within the membrane112 to expand, such as by 10% in the case of water being containedwithin the frame 102. The membrane 112 is configured to seal the frame102 to define the chamber 104 such that a fluid, such as water, will becontained within the frame 102. In some embodiments, the frame may forman open top such that the water is exposed to the ambient air. In otherembodiments, the frame may include an optional and/or removable top orcap that may be configured to fluidly contain the water within thechamber 104.

An operating fluid may be configured to pass into the heat exchanger 100and specifically, the operating fluid may be pumped, pass, or flowthrough the heat exchange elements 106, with the heat exchange element106 moveably retained within the frame 102. As such, the operating fluidmay pass through an inlet manifold 114 and into one or more flexiblehoses 116. The operating fluid will then enter the heat exchangeelements 106 to be in thermal contact with the phase-change material(water) contained within the chamber 106 of the frame 102. The operatingfluid will then exit the heat exchanger 100 at outlet 120, which mayinclude one or more flexible hoses and an outlet manifold (not shown).

In operation, to form an ice bath within the chamber 104, a coldoperating fluid may be pumped or passed from the inlet manifold 114,which may be on the bottom or lower portion of the heat exchanger 100,through the heat exchanger 100 and to an outlet, which may be on the topor upper portion of the heat exchanger 100. Thus, a cold operating fluidmay be introduced at the bottom of the heat exchanger 100 and may be ofsufficiently low temperature to cause a phase change in the watercontained in the chamber 104. For example, when the operating fluidenters at the inlet manifold 114 with the phase-change material beingwater, ice may begin to form at the bottom of the frame 102. This willform or create freeze progression through the heat exchange 100 thatbegins at the bottom and expands upward. As shown in FIG. 1, theconfiguration of the frame 102 has a narrower bottom and a wider topwhich is configured to accommodate the volumetric expansion of the wateras it freezes. That is, the frame 102 may define a tapered geometrywherein the base is narrower than the top, or the base may define asmaller area than the top.

In some embodiments, the heat exchanger 100 may be configured to employthe cooling of an operating fluid using sensible heat transfer. In otherembodiments, the heat exchanger 100 may be configured to have theoperating fluid (in addition to the phase-change material within thechamber 104) to experience a phase change. For example, the operatingfluid may be configured to condense during an ice-melt cycle and thenact as an evaporator during a freeze cycle.

Once the water is frozen, the phase-change material heat exchanger isready to cool an operating fluid rapidly. For example, after the ice isformed, the operating fluid may be used to cool a high temperatureapplication by absorbing thermal energy and carrying it away from thehigh temperature application. The heated operating fluid may be conveyedaway from the high temperature application to the heat exchanger 100. Asthe hot operating fluid enters the heat exchanger 100, the ice may beconverted back to water, thus absorbing high amounts of thermal energyfrom the hot operating fluid. This results in a rapidly cooled operatingfluid. After completion and the ice has turned to water, the process maybe repeated, with a cold operating fluid used to convert the water toice.

Turning now to FIG. 2, an alternative embodiment of a phase-changematerial heat exchanger is shown. In FIG. 2, a phase-change materialheat exchanger 200 is shown. The schematic shown in FIG. 2 also depictsthe flow path of an operating fluid, indicated in part by the arrows.The phase-change material heat exchanger 200 includes a frame 202configured to be filled by a phase-change material such as water. Theframe 202 may have a similar construction as the frame 102 of FIG. 1,including a membrane and/or cover. Contained within the frame 202 andsubmerged within the water may be one or more heat exchange elements204. As shown in FIG. 2, in contrast to the embodiment shown in FIG. 1,the heat exchange elements 204 are configured with a vertical separationor are vertically stacked heat exchange elements 204.

An operating fluid may flow through a flow path 206, either as a hotfluid or as a cold fluid, depending on the phase change to be achievedwithin the phase-change material. The operating fluid may be conveyedthrough the flow path 206 by means of a fluid pump 208. The fluid pump208 may pump the operating fluid into a heating and cooling element 210.The heating and cooling element 210 includes a coolant tank 212 and aheater 214. If the water is to be converted to ice, the coolant tank 212may be used to bring the operating fluid down to a temperaturesufficient to freeze water. However, if the ice is to be converted towater, the heater 214 may be used to warm the operating fluid. Thus, insome embodiments, the heater 214 may be thermally connected to a highenergy application, such as a laser, that may require rapid cooling.Heating and cooling element 210, as depicted in FIG. 2, is merelyrepresentative and those of skill in the art will appreciate that theheating and cooling elements of the phase-change material heat exchanger200 may be more than a single element, with the heating element(s)separate and distinct from the cooling element(s). In some embodiments,with separate heating and cooling elements, the elements may be in fluidcommunication or may be fluidly isolated from each other, depending onthe desired configuration and particular system employed.

After passing through the heating and cooling element 210, the operatingfluid may be conveyed into the frame 202 and the heat exchange elements204 contained therein. The operating fluid will then exit the heatexchange elements 204 and the frame 202 and then flow back to the pumpfor continuous operation.

Along the flow path 206 may be one or more thermal gages 216. Thethermal gages 216 may be configured to monitor the temperature of theoperating fluid within the flow path 206, monitor the temperature withinthe heating and cooling element 210, and/or be configured to monitor thetemperature of the phase-change material within the frame 202.Additionally, one or more flow meters 218 may be configured along theflow path 206 to monitor the flow rate of the operating fluid throughthe flow path 206 and may monitor the flow rate of the operating fluidinto the frame 202/heat exchange elements 204, as shown in FIG. 2.

Turning now to FIG. 3, a schematic of a heat exchange element inaccordance with embodiments of the disclosure is shown having a partialcut-away showing an interior thereof. Heat exchange element 300, asshown, is a plate-type heat exchange element that is configured to havea fluid pass through a body 302 of the heat exchange element 300. Asecond fluid, such as a phase-change material may be in fluid contactwith an exterior of the body 302. The body 302 of the heat exchangeelement 300 is configured to prevent fluid communication through thebody 302, thus fluidly separating the two media, but allowing thermalcommunication between the media.

The heat exchange element 300 includes a first support 304 and a secondsupport 306, with the body 302 extending therebetween. The first support304 and the second support 306 may each be hollow supports that allowfor fluid the pass through the interior of the supports 304, 306 or aportion of the interior of the supports 304, 306. An operating fluid mayenter the heat exchange element 300 at an inlet 308 that is on the firstsupport 304. The operating fluid may then pass through the body 302 ofthe heat exchange element 300. The operating fluid may then exit theheat exchange element 300 through an outlet (not shown) that isconfigured on the second support 306. The inlet 308 and the outlet maybe positioned on opposite ends of the heat exchange element 300.

The first support 304 and the second support 306 may each contain mounts310 that are configured to enable the heat exchange element 300 to bemounted within a frame, similar to that shown in FIGS. 1 and 2. Themounts 310 may be configured to be retained by or engage expansionelements, such as springs, wires, and/or rod elements, thus allowing theheat exchange element 300 to move within the frame.

In FIG. 3, the operating fluid may move from the bottom of the page tothe top of the page, with the operating fluid exiting the heat exchangeelement 300 at the top right portion on the page. Thus, the operatingfluid flow will start at the base or bottom of the page and thenprogress upward. This enables a controlled or directed freeze front asphase-change material that is in contact with an exterior of the heatexchange element 300 changes phase, e.g., from a liquid to a solid or asolid to a liquid.

Also shown in FIG. 3 is a cut-away 312 interior view of the body 302. Asshown, the cut-away 312 shows the structure of the interior of the body302. The interior of the body 302 may be formed with one or morechannels 314 that are configured to direct the operating fluid as itpasses through the body 302 of the heat exchange element 300. Thechannels 314 as shown run from left to right on the page, but it will beappreciated that the channels may be configured to run from bottom totop, or in some other manner, without departing from the scope of thedisclosure.

The structure of the body 302 may include a plurality of surface areastructures 316 housed between parting sheets 318 (only a portion of theparting sheet 318 is shown for illustrative purposes). The surface areastructures 316, in some embodiments, may be configured as fins. That is,fins or folds may be housed beneath parting sheets so that the surfacearea is maximized.

As shown, the surface area structures 316 may include a plurality ofperforations 320. The perforations 320 may be holes, apertures, etc.that allow the operating fluid to be directed through the body 302 ofthe heat exchange element 300. In some embodiments, the parting sheets318 may be omitted allowing direct fluid contact between an operatingfluid and a phase-change material at the surface of the surface areastructures 316. However, in such embodiments, the perforations 320 mustalso be omitted to prevent fluid mixing of the two media.

The configuration of surface area structures 316 and/or perforations 320may be configured to control the freeze front as it passes along thebody 302. For example, the number of surface area structures 316 perinch (e.g., surface area structure density) within the body may allowthe amount of thermal contact to be controlled by controlling ordefining the surface area of contact. Thus, the heat exchange element300 may be configured to direct a freeze front within a frame or tank,such as shown in FIGS. 1 and 2. In some embodiments, the surface areastructure density may be greatest in the center of the body 302,encouraging the phase-change material to solidify (change to ice) in thecenter and grow outward. The growth of the ice is the freeze front. Insome embodiments, in combination with or instead of a central start tothe freeze front, the operating fluid may be introduced at the bottom ofthe heat exchanger element 302 and encourage a freeze front that expandsupward relative to the heat exchange element 302.

A controlled freeze front is one factor that enables water to be used asthe phase-change material in a phase-change material heat exchanger. Bydefining where the ice will form first, pockets or trapped water may beprevented, thus eliminating the risk posed by ice forming within anenclosed space and causing damage. Further, by allowing the heatexchange elements to be moveable with respect to each other, as the iceexpands, the heat exchange elements may not impeded the expansion of theice along the freeze front.

Turning now to FIGS. 4A-4D, various configurations of surface areastructures in accordance with various embodiments are shown. FIG. 4Ashows the surface area structures configured as perforated folds orfins. Due to the perforations, partings sheets (not shown) may be placedon the exterior or peaks of the folds or fins to prevent fluid mixing.

FIG. 4B shows the surface area structures configured as extended fins.In FIG. 4B, the fins extend further away from a central body than thefins shown in FIG. 4A. In FIG. 4C the surface area structures areconfigured as a plurality of pins. In FIG. 4D the surface areastructures are configured as enhanced pins, having a larger threedimensional structure than the pins shown in FIG. 4C. The variousconfigurations shown in FIGS. 4A-4D are merely for illustrativepurposes, and those of skill in the art will appreciate that the surfacearea structures may take any form, shape, geometry, configuration,density, etc., without departing from the scope of the disclosure.

Turning now to FIG. 5, a process in accordance with the disclosure isshown. Process 500 is a method for employing water as a phase-changematerial in a phase-change material heat exchanger. At step 502, anoperating fluid at a first temperature is pumped into a phase-changematerial heat exchanger. The phase-change material in the phase-changematerial heat exchanger is water, and the operating fluid at the firsttemperature is at a temperature sufficiently low to freeze the water,i.e., convert the liquid water to solid ice.

As the operating fluid is pumped into the heat exchanger, at step 504 afreeze front is caused to form such that the water in the heat exchangermay freeze into ice, thus expanding, without damaging the heatexchanger. The freeze front is configured or formed such that thevolumetric expansion of the water turning to ice is accommodated for.

At step 506, the operating fluid, now at a second temperature that iswarmer than the first temperature, is conveyed out of the heatexchanger, and the heat exchanger is filled with solid ice.

At step 508, operating fluid at a third temperature may be pumped orconveyed into the heat exchanger. The third temperature may besufficiently hot to melt ice, thus converting the ice back to water.

At step 510, the operating fluid now at a fourth temperature is conveyedout of the heat exchanger. The fourth temperature is lower than thethird temperature.

It will be appreciated that the process 500 may employ a heat exchangerthat is similar to that described above and shown in FIGS. 1 and 2.Further, the process may employ surface area structures, as describedabove, to assist in generating and controlling a freeze front tocompensate for the volumetric expansion of water as it is converted toice. Furthermore, the heat exchange elements within the heat exchangerused in the process 500 may be similar to that described above andconfigured to be moveable relative to each other to further compensatefor the volumetric expansion of the water as it is converted to ice.

It will be appreciated that the above heat exchangers and processes aredescribed with respect to forming ice within a chamber from liquidwater, but that the opposite transition is also important. That is, oncethe ice is formed, it will be ready to absorb thermal energy from a hotoperating fluid. As noted above, the latent heat of ice is significantlyhigher than the latent heat of wax, which has been traditionally used inphase-change material heat exchangers. As such, when ice is containedwithin the chamber of the heat exchanger, the operating fluid, at a veryhigh temperature, may be passed through the heat exchanger and the icemay be melted, changing the phase of the water from a solid to a liquidby the absorption of thermal energy from the operating fluid.

Advantageously, embodiments described herein provide a phase-changematerial heat exchanger that employs water/ice as the phase-changematerial. Further, advantageously, embodiments described herein allowfor a 225% increase in volume efficiency over wax-based phase-changematerial heat exchangers. That is, for the same amount of thermalcooling, a much smaller heat exchanger may be used, or in contrast,based on the same size, a much larger or faster cooling may be achievedwith embodiments described herein. For example, the heat exchangervolume may be reduced by about 60% when embodiments disclosed herein areemployed, over wax-based heat exchangers.

Further, advantageously, embodiments described herein allow for easymaintenance because water is a readily available and non-toxic resourcethat may be easily replenished, flushed from the system, etc.

While the present disclosure has been described in detail in connectionwith only a limited number of embodiments, it should be readilyunderstood that the present disclosure is not limited to such disclosedembodiments. Rather, the present disclosure can be modified toincorporate any number of variations, alterations, substitutions,combinations, sub-combinations, or equivalent arrangements notheretofore described, but which are commensurate with the spirit andscope of the present disclosure. Additionally, while various embodimentsof the present disclosure have been described, it is to be understoodthat aspects of the present disclosure may include only some of thedescribed embodiments.

For example, although shown and described with respect to a plate-typeheat exchanger, those of skill in the art will appreciate that ashell-and-tube heat exchanger may be configured by employing embodimentsand configurations disclosed herein. In some shell-and-tube heatexchanger configurations, the heat exchanger may be configured to floatwithin an ice/water bath similar to the plate-fin heat exchangerdiscussed herein.

Accordingly, the present disclosure is not to be seen as limited by theforegoing description, but is only limited by the scope of the appendedclaims.

What is claimed is:
 1. A phase-change material heat exchanger comprising: a frame configured to define a chamber therein and house a first fluid, the first fluid being water; and at least one heat exchange element configured to have a second fluid pass through an interior of the heat exchange element, the at least one heat exchange element moveably retained within the chamber; wherein when the second fluid passes through the heat exchange element at a first temperature, the first fluid changes from a liquid to a solid, and the second fluid exits the heat exchange element at a second temperature that is higher than the first temperature.
 2. The heat exchanger of claim 1, wherein the at least one heat exchange element includes a plurality of surface area structures on an exterior surface thereof.
 3. The heat exchanger of claim 2, wherein the plurality of surface area structures are at least one of fins and pins.
 4. The heat exchanger of claim 1, wherein the at least one heat exchange element has a plate configuration.
 5. The heat exchanger of claim 1, wherein the at least one heat exchange element is configured to define a freeze front of the first fluid along an exterior surface of the at least one heat exchange element.
 6. The heat exchanger of claim 1, wherein the second fluid is an operating fluid for a high powered laser.
 7. The heat exchanger of claim 1, wherein the frame defines a tapered shape with a bottom of the frame being narrower than a top of the frame.
 8. The heat exchanger of claim 1, further comprising at least one expansion element configured to support the at least one heat exchange element within the chamber.
 9. The heat exchanger of claim 8, wherein the at least one expansion element is a spring.
 10. The heat exchanger of claim 1, further comprising a membrane retained about the frame and configured to expand when the first fluid changes from a liquid to a solid.
 11. The heat exchanger of claim 1, wherein the at least one heat exchange element comprises a first support and a second support, with a body extending between the first support and the second support.
 12. The heat exchanger of claim 1, further comprising an enclosure, wherein the enclosure includes the frame and at least a portion of the enclosure is configured to expand in response to water freezing.
 13. A method of using a phase-change material heat exchanger, the method comprising: conveying an operating fluid at a first temperature through at least one heat exchange element, the at least one heat exchange element disposed within a chamber of a phase-change material heat exchanger, the chamber filled with water; causing the water to phase change from a liquid to a solid within the chamber; and conveying the operating fluid out of the at least one heat exchange element at a second temperature that is higher than the first temperature.
 14. The method of claim 13, the method further comprising conveying the operating fluid through the at least one heat exchange element at a third temperature when the chamber is filled with ice.
 15. The method of claim 14, wherein the third temperature is a temperature sufficiently high to phase change the ice to liquid water when passing through the at least one heat exchange element.
 16. The method of claim 13, further comprising forming a freeze front progression within the chamber such that a volumetric expansion of the water when freezing does not damage the phase-change material heat exchanger. 